First attempt to place a one filter at source. Try to apply on helm-ff.
* helm-files.el: Fix ff sort function.
Rename filter attribute.
* helm-files.el (helm-ff-filter-candidate-one-by-one): Handle tramp files.
* helm-help.el: Document filter-one-by-one.
* helm.el: Add comment.
* helm.el (helm-match-from-candidates): Allow more than one function in filter-one-by-one.
* helm-mode.el (helm-read-file-name): Use filter-one-by-one and sort.
* helm-files.el: Remove now unused transformer function and var.